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In investing, beware the halo effectPeople frequently–and incorrectly–attribute wonderful characteristics to something that has succeeded. Just because something has succeeded does not necessarily mean it’s specifc attributes are also excellent.

This issue is succinctly highlighted in the third part of Michael Mauboussin’sLegg Mason article.

The “halo effect is the human proclivity to make specific inferences based on general impressions.” This was first noted over 80 years ago by psychologist Edward Thorndike and was recently described in detail in Phil Rosenzweig’s book, The Halo Effect.

What Thorndike found by studying military officer reviews was that superiors tended to attribute overwhelmingly positive specific attributes to subordinate officers who they had good overall impressions of. In other words, they assigned impossibly high ratings to their intelligence, physique, leadership, etc. based on their high overall opinion.

This tendency can be particularly dangerous in picking investments. Those who attribute outstanding specific characteristics to Apple or Google simply because they have done well in the past and everyone seems to love them may be in for a rude surprise if they invest in these companies at current prices.

The same can be true on the downside as well. People tend to assume that companies whose stock has performed poorly or whose profitability has lagged have universally negative specific characteristics. This is unlikely to always be the case.

People tend to assume that popular stocks have great specific attributes, reflecting popularity more than excellence. When an inevitable blemish appears, the stock tanks because it was priced for perfection

In reverse, people tend to assume that unpopular stocks have universally negative attributes. When it turns out the business isn’t as bad as everyone believed, the stock takes off because it was priced for bankruptcy.

In selecting investments, it’s very important to gain a clear view. Popularity is no way to judge an investment. Look critically at every investment opportunity, no matter how much people love it. And, companies that everyone things are doing poorly may be a great place to invest because good characteristics may have been overlooked.

To avoid the halo effect, look for disconfirming evidence–evidence that conflicts with the popular view. Work hard to understand both the good and bad characteristics of an investment. This will help you rationally assess its prospects, and almost certainly lead to better investment results.Nothing in this blog should be considered investment, financial, tax, or legal advice. The opinions, estimates and projections contained herein are subject to change without notice. Information throughout this blog has been obtained from sources believed to be accurate and reliable, but such accuracy cannot be guaranteed.